This invention relates to a tone waveshape generation device employed in an electronic musical instrument and, more particularly, to a device capable of reading out repetitively waveshape of plural periods stored in a memory.
An electronic musical instrument of a type in which a complete waveshape from the start to the end of generation of a tone is prestored for each key (note) and this waveshape is read out is disclosed in the spedification of U.S. Pat. No. 4,383,462. In the waveshape memory WM31 shown in FIG. 3 of this United States patent, a complete waveshape is stored and this complete waveshape is read out in response to a signal KD which represents a key depression timing. This type of instrument storing all waveshapes however is disadvantageous in that it requires a memory having a large memory capacity resulting in high manufacturing cost and also that production of a sustained tone is practically impossible.
For overcoming these disadvantages, it has been proposed to store a part of waveshape of plural periods in the entire tone production period in a waveshape memory and produce a tone signal by repeatedly reading out this waveshape portion. There is a problem in this proposed system that mere continuation of the repeatedly read out waveshape portion of plural periods gives rise to unnaturalness in connecting points of repeatedly read out portions. Further, an attack portion of a tone generally changes in a complicated manner thereby exhibiting a great difference from a relatively stable waveshape in the sustain portion. For producing a tone of a good quality, therefore, a waveshape of plural periods of the attack portion should be prepared in addition to a waveshape of plural periods which is to be read out repeatedly and this attack portion should be read once before repetitive readout of the repetitive portion. Even in this case it is necessary to make an arrangement to avoid unnaturalness in the connecting point between the attack portion and the repetitive portion.
In the above U.S. Pat. No. 4,383,462, an example of such tone waveshape generation by repetitive readout is shown in FIG. 6. A complete waveshape in the attack portion is stored in the waveshape memory WM61 and at least one fundamental period of a tone waveshape is stored in the waveshape memory WM62. An attack waveshape is read out from the memory WM61 response to the key depression (KD signal) and the tone waveshape of the fundamental period is repeatedly read out from the memory WM62 after completion of the read out of the attack waveshape (IMF signal) until the end of tone generation (DF signal). In this example, however, no consideration has been given to smoothing of the connection of the end of the waveshape of the attack portion and the beginning of the waveshape of the fundamental period. Neither has any consideration been given to smoothing of the connection between the repeatedly read out fundamental periods.